Tunable impedance network

Abstract

A tunable impedance network and a method for tuning the tunable impedance network are disclosed. In one aspect, the tunable impedance network comprises a plurality of transformers connected in series. Each transformer has a primary winding and a secondary winding. The transformers have a voltage transformation ratio of N:1 with N>1. An impedance structure, acting as a resonant circuit together with the inductance of the secondary winding, is connected at the secondary winding of each transformer. A control circuit or processor is configured to tune the imaginary part of at least one of the impedance structures so as to change its resonance frequency to mimic a reference impedance. The control circuit is further configured to tune the real part of at least one of the impedance structures so as to change its Q-factor to mimic the reference impedance.

What is claimed is: 
     
       1. A tunable impedance network comprising:
 a plurality of transformers connected in series, each of the transformers having a primary winding and a secondary winding, each of the transformers configured to transform a voltage by a voltage transformation ratio of N:1 with N>1; 
 a plurality of impedance structures, each of the impedance structures connected at the secondary winding of each of the transformers, each of the impedance structures configured to act as a resonant circuit together with the inductance of the secondary winding, wherein at least one of the impedance structures is a tunable passive network comprising at least one tunable resistor circuit and at least one tunable capacitor circuit, wherein each of the tunable resistor circuit and the tunable capacitor circuit comprise at least one transistor circuit. 
 
     
     
       2. The tunable impedance network of  claim 1 , further comprising a control circuit configured to tune the imaginary part of at least one of the impedance structures so as to change its resonance frequency to mimic a reference impedance, the control circuit further configured to tune the real part of at least one of the impedance structures so as to change its Q-factor to mimic the reference impedance. 
     
     
       3. The tunable impedance network of  claim 1 , wherein the at least one transistor circuit comprises a variable resistor or a variable capacitor. 
     
     
       4. The tunable impedance network of  claim 1 , wherein the at least one tunable resistor circuit comprises a bank of parallel switched resistors and the at least one tunable capacitor circuit comprises a bank of parallel switched capacitors, wherein the bank of parallel switched resistors comprises a first plurality of transistors configured as switches, wherein the bank of parallel switched capacitors comprises another plurality of transistors configured as switches. 
     
     
       5. The tunable impedance network of  claim 1 , wherein the impedance of at least one of the impedance structures has a real and an imaginary part. 
     
     
       6. The tunable impedance network of  claim 1 , wherein the tunable passive network comprises at least one series or parallel connected inductor. 
     
     
       7. The tunable impedance network of  claim 1 , wherein the transformation ratio is the same for each of the transformers. 
     
     
       8. The tunable impedance network of  claim 1 , wherein the impedance structures are equal for each of the transformers. 
     
     
       9. The tunable impedance network of  claim 1 , wherein at least one of the impedance structures is different from the other impedance structures. 
     
     
       10. The tunable impedance network of  claim 1 , wherein the at least one transistor circuit is implemented in CMOS technology. 
     
     
       11. An electrical balance duplexer comprising a tunable impedance network according to  claim 1  configured to balance impedance with an antenna. 
     
     
       12. A circuit comprising:
 an antenna; 
 a power amplifier; and 
 a tunable impedance network according to  claim 1  configured for antenna matching. 
 
     
     
       13. A tunable band-pass filter comprising a tunable impedance network according to  claim 1  configured to band-pass filter over the outer terminals of the series of connected first windings. 
     
     
       14. A method of tuning the impedance of a tunable impedance network to a reference impedance having a real and imaginary part, the tunable impedance network comprising a plurality of transformers connected in series, each transformer having a primary winding and a secondary winding, the transformers having a voltage transformation ratio of N:1 with N>1, with connected at the secondary winding of each transformer an impedance structure acting as a resonant circuit together with the inductance of the secondary winding, at least one of the impedance structures being a tunable passive network comprising at least one tunable resistor circuit and at least one tunable capacitor circuit, wherein each of the tunable resistor circuit and the tunable capacitor circuit comprise at least one transistor circuit, the method comprising:
 tuning the imaginary part of at least one of the impedance structures so as to change its resonance frequency to mimic the reference impedance; and 
 tuning the real part of at least one of the impedance structures so as to change its Q-factor to mimic the reference impedance. 
 
     
     
       15. The method of  claim 14 , wherein tuning comprises separately tuning different impedance structures. 
     
     
       16. The method of  claim 14 , comprising independently changing the resonance frequency and Q factor of the tunable impedance network. 
     
     
       17. Method according to  claim 14 , further comprising retuning the impedance structures during operation. 
     
     
       18. An integrated circuit comprising:
 a tunable impedance network comprising: 
 a plurality of transformers connected in series, each of the transformers having a primary winding and a secondary winding, each of the transformers configured to transform a voltage by a voltage transformation ratio of N:1 with N>1; 
 a plurality of impedance structures, each of the impedance structures connected at the secondary winding of each of the transformers, each of the impedance structures configured to act as a resonant circuit together with the inductance of the secondary winding, wherein the impedance structure is a tunable passive network comprising at least one tunable resistor circuit and at least one tunable capacitor circuit, wherein each of the tunable resistor circuit and the tunable capacitor circuit comprise at least one transistor circuit; and 
 a processor configured to tune the tunable impedance network according to  claim 14 . 
 
     
     
       19. A tunable impedance network comprising:
 a plurality of transformers connected in series each of the transformers having a primary winding and a secondary winding, each of the transformers configured to transform a voltage by a voltage transformation ratio of N:1 with N>1; 
 a plurality of impedance structures, each of the impedance structures connected at the secondary winding of each of the transformers, each of the impedance structures configured to act as a resonant circuit together with the inductance of the secondary winding, wherein at least one of the impedance structures is a tunable network comprising at least one tunable resistor circuit and at least one tunable capacitor circuit, wherein each of the tunable resistor circuit and the tunable capacitor circuit comprise at least one transistor circuit, wherein at least one of the impedance structures further comprises at least one active component. 
 
     
     
       20. A tunable impedance network comprising: means for transforming an input series of voltages to an output series of voltages by a voltage transformation ratio of N:1 with N>1, comprising a plurality of transformers; and means for tuning an impedance of each of a series of impedance structures of the transforming means, comprising a series of tunable passive networks, the means for tuning an impedance comprising: means for tuning the imaginary part of at least one of the impedance structures so as to change its resonance frequency to mimic a reference impedance, comprising a control circuit; and means for tuning the real part of at least one of the impedance structures so as to change its Q-factor to mimic the reference impedance, comprising the control circuit.